Conventionally, a fiber-reinforced plastic sheet which is produced by arranging fiber-reinforced plastic strands produced using reinforcing fiber, such as carbon fiber, in the form of sheet has been widely applied in, for example, RTM, as a large-sized FRP (fiber reinforced plastic) used for, for example, blades for windmills, vehicles, and vessels. Furthermore, such fiber-reinforced plastic sheet has been also applied as a reinforcement which adheres to and thereby reinforces civil-engineering structures such as a concrete structure, a steel structure, and a fiber-reinforced plastic structure.
Here, in the case where a fiber-reinforced plastic sheet is used for, for example, RTM, or in the case where a fiber-reinforced plastic sheet is used to be bonded to a structure, such as a concrete structure or a steel structure, thereby reinforcing the structure, if fiber-reinforced plastic strands which constitute the fiber-reinforced plastic sheet have a round shape, the plate thickness (that is, reinforcement thickness) is thicker, and the amount of adhering resin is larger. On the other hand, when the fiber-reinforced plastic strands have a flat shape, the same reinforcement strength as that obtained in the case of using the round fiber-reinforced plastic strands can be achieved with a thinner reinforcement thickness and a smaller amount of adhering resin.
Furthermore, also in the case where a fiber-reinforced plastic strand is used as a reinforcement bar embedded in, for example, a concrete structure or a glass-fiber-reinforced plastic structure, the fiber-reinforced plastic strand having a flat shape allows the plate thickness of a portion in which the reinforcement bar is embedded to be thinner, and accordingly allows more reinforcing fibers to be fed within a certain plate thickness, and, compared to a round strand, the flat strand allows a fiber content within a certain volume (that is, Vf) and targets for the cross section stiffness and strength of a structure to be achieved with a thinner plate thickness.
However, in the case where a fiber-reinforced plastic strand having a flat shape, that is, a flat fiber-reinforced plastic strand is produced by pultrusion forming process as is the case with the producing of a round strand, there are a restriction on die and a restriction on the number of strands to be manufactured due to a limit in the number of holes. Furthermore, a problem is encountered in that use of a release agent is indispensable for preventing a matrix resin from sticking to a die, and bonding of a product obtained after forming to resin or concrete to be bonded later does not go well.
Patent Literatures 1 and 2 disclose:                (1) a manufacturing method wherein a reinforcing fiber bundle (strand) to be continuously fed is impregnated with a resin while being twisted, or a resin-impregnated strand which has been impregnated with a resin is twisted, and then, this resin-impregnated strand having been impregnated with the resin and twisted is given a prescribed tensile force, whereby a fiber-reinforced plastic strand having a round cross section is produced; and        (2) a manufacturing method wherein a plate-shaped die is used in order to make a resin-impregnated round strand containing an uncured resin into a plate-shaped strand, and the plate-shaped die is released from a flat strand product not by using a release agent, but by continuously interposing a thin cloth (for example, a polyester textile called as “peel ply”) which does not adhere to an adhesive into the top and bottom surfaces of strand to be formed, and peeling away the cloth after the resin is cured. Such manufacturing methods have advantages that it is beneficial to simply lead the resin-impregnated round fiber bundle into a plate-shaped die, and, since the top and bottom of the bundle are protected by the thin cloth for release and the resin-impregnated fiber bundle does not directly touch the die accordingly, the resin-impregnated fiber bundle is less damaged, thread breakage during manufacturing occurs with far less frequency, and forming yields can be considerably increased, accordingly.        